Air conditioner and method for controlling of air conditioner

ABSTRACT

An air conditioner includes first and second air passages, first and desiccant devices, a system heat source, a heat supplier, a system heat source temperature sensor, an airflow controller and a controller. The first and second air passages are communicable with a space to be air conditioned. The first desiccant device disposing in the first air passage has a first desiccant material. The second desiccant device disposed in the second air passage has a second desiccant material whose temperature for regeneration is higher than the temperature for regeneration of the first desiccant material. The heat supplier supplies heat generated by the system heat source to the first desiccant device for regenerating the first desiccant material. The airflow controller regulates airflow in the first and second air passages. The controller controls the airflow controller based on the temperature of the system heat source detected by the system heat source temperature sensor.

BACKGROUND OF THE INVENTION

The present invention relates to an air conditioner for a vehicle and amethod for controlling of the air conditioner.

A conventional air conditioner for a vehicle is disclosed in JapanesePatent Application Publication No. 2004-177074. Referring to FIG. 12,the air conditioner has a first air passage 107, a second air passage108, a first desiccant rotor 101, a second desiccant rotor 102 and asensible heat exchanger 103. The first air passage 107 includes asuction passage 105 and a discharge passage 106. The first desiccantrotor 101 has a first dehumidifier 121 in the suction passage 105thereof and a dehumidifier-cooler 122 in the discharge passage 106thereof. The second desiccant rotor 102 includes a second dehumidifier123 in the suction passage 105 thereof and a regenerating part 124 inthe second air passage 108 thereof. Air flowing from the vehicleinterior is dehumidified in the first dehumidifier 121 and the seconddehumidifier 123, cooled in the sensible heat exchanger 103, humidifiedand cooled in the dehumidifier-cooler 122 and then supplied to thevehicle interior.

Air flowed into the air passage 107 is dehumidified in the firstdehydrator 121 of the first desiccant rotor 101 and then furtherdehumidified in the second dehydrator 123 of the second desiccant rotor102. Thus, the air to be dehumidified by the first desiccant rotor 101has a relatively high humidity, while the air to be dehumidified by thesecond desiccant rotor 102 has been already dehumidified by the firstdehumidifier 121 and, therefore, has a relatively low humidity.Therefore, appropriate materials suitable for the respective humidityranges of the air can be used in the desiccant rotors 101, 102 foreffective utilization of the desiccant rotors 101, 102. The ranges oftemperature under which the first desiccant rotor 101 and the seconddesiccant rotor 102 are operated are different from each other. Thus,the first and second desiccant rotors 101, 102 are used undertemperatures of different ranges, so that the heat loss due to a changeof temperatures of the desiccant rotors 101, 102 is reduced.

In the desiccant rotor used in the above conventional air conditioner,heat loss of the desiccant rotor due to the change of the temperature ofthe desiccant rotor can be reduced. However, in a vehicle which ispowered only by a battery during at least a certain period of time, suchas an electric vehicle or a plug-in hybrid vehicle (these vehicleshereinafter being referred to merely as “PHEV”), the temperature ofexhaust heat generated by system heat sources such as an inverter islower than the temperature of exhaust gas heat generated by the vehicleengine. Therefore, air having a high temperature for regenerating thedesiccant rotor is not generated, so that the desiccant rotor cannot beregenerated for repeated dehumidification.

The present invention is directed to providing an air conditioner bywhich air can be repeatedly dehumidified when the temperature of exhaustheat is low and a method for controlling the air conditioner.

SUMMARY OF THE INVENTION

In accordance with the present invention, an air conditioner includesfirst and second air passages, first and second desiccant devices, asystem heat source, a heat supplier, a system heat source temperaturesensor, an airflow controller and a controller. The first air passagehas a first inlet and a first outlet communicable with a space to be airconditioned. The first desiccant device has a first desiccant materialand is disposed in the first air passage. The second air passage has asecond inlet and a second outlet communicable with the space. The seconddesiccant device has a second desiccant material whose temperature forregeneration is higher than the temperature for regeneration of thefirst desiccant material and is disposed in the second air passage. Theheat supplier supplies heat generated by the system heat source to thefirst desiccant device for regenerating the first desiccant material.The system heat source temperature sensor detects the temperature of thesystem heat source. The airflow controller regulates airflow in thefirst air passage and the second air passage. The controller controlsthe airflow controller based on the temperature of the system heatsource detected by the system heat source temperature sensor.

Other aspects and advantages of the invention will become apparent fromthe following description, taken in conjunction with the accompanyingdrawings, illustrating by way of example the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention together with objects and advantages thereof, may best beunderstood by reference to the following description of the presentlypreferred embodiments together with the accompanying drawings in which:

FIG. 1 is a plane view showing the structure of an electric vehiclehaving an air conditioner according to a first preferred embodiment ofthe present invention;

FIG. 2 is a system diagram of the air conditioner of FIG. 1;

FIG. 3 is a flowchart showing steps of operation for controlling thedehumidification in accordance with the condition of the dehumidifyingload and exhaust heat in the air conditioner of FIG. 1;

FIG. 4 is a temperature data map showing a relation between thetemperatures of external air and the exhaust heat in the air conditionerof FIG. 1.

FIG. 5A is a system diagram of the air conditioner of FIG. 1 explainingdehumidification performed only by a first desiccant device of the airconditioner;

FIG. 5B is a system diagram of the air conditioner of FIG. 1 explainingdehumidification performed by the combination of the first and seconddesiccant devices;

FIG. 5C is a system diagram of the air conditioner of FIG. 1 explainingdehumidification performed only by the second desiccant device of theair conditioner;

FIG. 5D is a system diagram of the air conditioner of FIG. 1 explainingregeneration of the second desiccant device of the air conditioner;

FIG. 6A is a system diagram of the air conditioner of FIG. 1 explainingregeneration of the first desiccant device of the air conditioner whendehumidification is performed by the second desiccant device;

FIG. 6B is a system diagram of the air conditioner of FIG. 1 explainingregeneration of the first desiccant device when dehumidification is notperformed;

FIG. 7A is a system diagram of an air conditioner according to a secondpreferred embodiment of the present invention;

FIG. 7B is the fragmentary diagram of the air conditioner of FIG. 7A inwhich three-way valves are used instead of a valve;

FIG. 8A is a system diagram of an alternative air conditioner accordingto the second preferred embodiment of the present invention;

FIG. 8B is an fragmentary diagram of the air conditioner of FIG. 8A inwhich three-way valves are used instead of a valve;

FIG. 9 is a system diagram of an air conditioner according to a thirdpreferred embodiment of the present invention;

FIG. 10 is a system diagram of the air conditioner of FIG. 9 explainingheating of the vehicle interior by using air generated by regenerationof the second moisture absorber;

FIG. 11 is a system diagram of the air conditioner of FIG. 9 explainingheating of the vehicle interior by using air generated by regenerationof the first moisture absorber; and

FIG. 12 is a system diagram of an air conditioner according to abackground art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe an air conditioner according to a firstpreferred embodiment of the present invention with reference to FIGS. 1through 6B.

Referring to FIG. 1, there is shown an air conditioner 20 mounted to anelectric vehicle 10. An electric motor 11, an inverter 12, an electriccontrol unit (ECU) 13 and an electric vehicle air conditioner(hereinafter referred to merely as “air conditioner”) 20 are disposed inthe front of the vehicle 10. The electric motor 11 serves as a powersource for driving the vehicle 10. The inverter 12 converts electricpower for supplying the electric power to the electric motor 11. The ECU13 controls the operation of various devices of the vehicle 10, such asthe inverter 12 and serves as a controller. The inverter 12 is connectedelectrically to the electric motor 11, the ECU 13 and the airconditioner 20 for supplying electric power. A battery 14 is mounted inthe rear of the vehicle 10. A first power line 15 is arranged in thevehicle 10 for electrically connecting the battery 14 with the inverter12. A second power line 16 is arranged in the vehicle 10 and connectedto the first power line 15. The second power line 16 is also connectedto a battery charger 17 which is connectable to an external power source18. Thus, the air conditioner 20 is used for the vehicle 10 having thebattery 14 charged by the external power generated by the external powersource 18 during a stop state of the vehicle 10.

Referring to FIG. 2, the air conditioner 20 has an air passage 21connecting an exterior S of the vehicle 10 as the exterior of the airconditioner 20 to an interior R of the vehicle 10 as the space to be airconditioned. The air passage 21 is a passage through which air for airconditioning of the interior R flows and has an inlet 21A communicablewith the exterior S and an outlet 21 B communicable with the interior R.A first desiccant device 22 is disposed in the air passage 21 as a firstmoisture absorbing device. A first blower 23 is disposed in the airpassage 21 between the first desiccant device 22 and the exterior S.

An air passage 24 is branched from the air passage 21 at a branch pointP between the first blower 23 and the first desiccant device 22 andconnected to the air passage 21 at a point Q between the first desiccantdevice 22 and the interior R. A second desiccant device 25 as a secondmoisture absorbing device is disposed in the branched air passage 24. Afirst valve 26 is disposed between the branch point P and the firstdesiccant device 22 in the air passage 21. A second valve 27 is disposedbetween the branch point P and the second desiccant device 25 in thebranched air passage 24. A first temperature sensor 28 is disposedbetween the first blower 23 and the exterior S in the air passage 21.The first temperature sensor 28 serves as an air temperature sensor. Thefirst temperature sensor 28 is used for measuring the temperature T1 ofthe air flowing adjacent to the first inlet 21A in the air passage 21 asthe temperature of the external air which is to be dehumidified. Inother words, the first temperature sensor 28 is used for measuring thetemperature T1 of the air flowing to the first desiccant device 22 inthe air passage 21 or to the second desiccant device 25 in the branchedair passage 24. The heater 33 is disposed between the second desiccantdevice 25 and the point Q in the branched air passage 24. The heater 33is operated to generate heat from electric power supplied by theexternal power source 18 as the external power for regenerating thesecond moisture absorber 252.

In the air conditioner 20 according to the first preferred embodiment ofthe present invention, the path of air flowing from the inlet 21Acommunicable with the exterior S through the branch point P, the firstdesiccant device 22 and the point Q to the outlet 21B communicable withthe interior R as the space to be air conditioned forms the first airpassage of the present invention. The path of air flowing from the inlet21A through the branch point P, the second desiccant device 25 and thepoint Q to the outlet 21B forms the second air passage of the presentinvention. Therefore, part of the air passage that extends from theinlet 21A to the branch point P is common to the first and the secondair passages, forming an exterior-side passage of the present invention.Similarly, part of the air passage that extends from the point Q to theoutlet 21B is common to the first and second air passages, forming anair conditioner-side passage of the present invention. The inlet 21Acommunicable with the exterior S serves as a first inlet of the firstair passage of the present invention and also a second inlet of thesecond air passage of the present invention. The outlet 21B communicablewith the interior R serves as a first outlet of the first air passage ofthe present invention and also a second outlet of the second air passageof the present invention. Thus, part of the air passage is common to theair passages 21, 24, and the remaining parts of the air passages 21, 24are arranged parallel to each other, or the inlet 21A and the inlet 21Aor the outlet 21B and the outlet 21B is common to each other and the airpassage 21 and the branched air passage 24 including the first desiccantdevice 22 and the second desiccant device 25 are arranged parallel toeach other.

An internal air passage 34 is arranged in the air conditioner 20 forcirculating air through the interior R. One end 34A of the internal airpassage 34 is communicable with the interior R and air in the interior Ris introduced into the internal air passage 34 through this end 34A. Theother end 34B of the internal air passage 34 is connected to the airpassage 21 at a point between the first temperature sensor 28 and thefirst blower 23. A third valve 35 is disposed in the internal airpassage 34 and its operation controlled by the ECU 13. A fourth valve 36is disposed between the inlet 21A and the first temperature sensor 28 inthe air passage 21 and its operation is controlled by the ECU 13. Incirculating air through the interior R while dehumidifying the air, thethird valve 35 is opened, the fourth valve 36 is closed, and at leastone of the first valve 26 and the second valve 27 is opened. When no airis circulated through the interior R, the third valve 35 is closed.

A humidity sensor 37A for measuring the humidity in the interior R and athird temperature sensor 38 for measuring the temperature in theinterior R are provided in the air conditioner 20 and connectedelectrically to the ECU 13. The third temperature sensor 38 serves as aspace air temperature sensor. The humidity sensor 37A is used indetermining whether or not dehumidification of air in the interior R isneeded. The third temperature sensor 38 is used for measuring thetemperature of air in the interior R in determining which of thedesiccant devices should be operated for dehumidifying the air in theinterior R. The first blower 23, the first valve 26, the second valve27, the third valve. 35 and the fourth valve 36 regulate airflow in theair passage 21 and the branched air passage 24 and form an airflowcontroller of the present invention.

The air conditioner 20 according to the first preferred embodiment ofthe present invention further includes an electric power device 19. Theelectric power device 19 includes the inverter 12 and the electric motor11, serving as the power source for the vehicle and a system heat sourcegenerating heat for regenerating a first moisture absorber 222 providedin the first desiccant device 22. The first moisture absorber 222 servesas a first desiccant material. The system heat source according to thefirst preferred embodiment of the present invention includes heatradiating devices radiating waste heat during the device operation onthe vehicle 10 excepting internal combustion engines such as a heaterand an engine which use electric power of battery. Specifically, theheat radiating devices include such vehicle-mounted components such asthe inverter 12, the electric motor 11, the battery 14, a gear, and abrake. A second temperature sensor 29 is provided in the electric powerdevice 19 for detecting the temperature T2 of exhaust heat generated bythe system heat sources in the electric power device 19. The secondtemperature sensor 29 serves as a system heat source temperature sensorof the present invention.

A regeneration air passage 30 is formed in the air conditioner 20 as aheat supplier of the present invention for supplying exhaust heatgenerated by the electric power device 19. The regeneration air passage30 communicates with the interior R and the exterior S and used fordischarging air in the interior R. The regeneration air passage 30 isconnected to the electric power device 19. The first desiccant device 22is also disposed between the electric power device 19 and the exterior Sin the regeneration air passage 30. A second blower 31 is disposedbetween the electric power device 19 and the interior R in theregeneration air passage 30.

The first desiccant device 22 is used for dehumidifying air introducedinto the air passage 21 by the first blower 23. The first desiccantdevice 22 includes a cylindrical case 221 accommodating therein thefirst moisture absorber 222 that is ratatable. The first moistureabsorber 222 has a property of absorbing moisture and releasing theabsorbed moisture when the temperature of the first moisture absorber222 reaches a predetermined temperature range. Mesoporous silica is usedfor the first moisture absorber 222. Mesoporous silica has a property ofperforming rapid dehumidification under a predetermined temperature andhumidity, and releasing the absorbed moisture when the temperature ofmesoporous silica increased to a temperature range from 50 through 60degrees so that the moisture absorber is regenerated for reuse. Moistureabsorbing property of the first desiccant device 22 is not higher ascompared to the second desiccant device 25, but the first desiccantdevice 22 has a characteristic of being regenerated under a relativelylow temperature in comparison to the second desiccant device 25. Thus,the first desiccant device 22 may be regenerated by exhaust heatgenerated in the electric power device 19 whose temperature isrelatively low.

The above-described moisture absorbing property of each of the first andsecond desiccant devices 22, 25 is determined by the temperature of airat which the respective desiccant devices 22, 25 can dehumidify. With anincrease of the moisture absorbing property of each of the first andsecond desiccant devices 22, 25, the first and second desiccant devices22, 25 may perform sufficient dehumidification if the temperature of theair to be dehumidified is relatively high. If each of the first andsecond desiccant devices 22, 25 has a relatively high moisture absorbingproperty, or the temperature of the air to be dehumidified by themoisture absorber of the first and second desiccant devices 22, 25 isrelatively high, the temperature for regenerating the moisture absorbertends to be high.

The first desiccant device 22 further includes an electric motor 223having a rotary shaft 224. The first moisture absorber 222 of the firstdesiccant device 22 is mounted on the rotary shaft 224 for rotationtherewith. The air passage 21 and the regeneration air passage 30through which air for regenerating flows are connected to the firstdesiccant device 22 at two opposite positions of the rotary shaft 224.Specifically, in the case of FIG. 2, the air passage 21 and theregeneration air passage 30 are connected to the first desiccant device22 at two opposite positions one above the other. Air is passed throughthe first moisture absorber 222 at the respective connections.Therefore, while the first desiccant device 22 is rotating,dehumidification of air flowing through the air passage 21 regenerationof the first moisture absorber 222 by the heat of the air flowingthrough the regeneration air passage 30 are simultaneously performed.

In the first preferred embodiment of the present invention, a humiditysensor 37B is disposed between the first desiccant device 22 and thepoint Q in the air passage 21 and connected electrically to the ECU 13.The humidity sensor 37B measures the humidity of the air dehumidified bythe first desiccant device 22. If the humidity of the dehumidified airexceeds a predetermined value because the regeneration of the firstmoisture absorber 222 by the exhaust heat of the system heat sourcescannot meet the dehumidifying demand, the ECU 13 determines that themoisture absorbing capacity of the first desiccant device 22 has reachedthe maximum value, thereby activating the second desiccant device 25.

The second desiccant device 25 is used for dehumidifying air in thebranched air passage 24. The second desiccant device 25 includes a case251 accommodating therein a second moisture absorber 252. The secondmoisture absorber 252 serves as a second desiccant material. The secondmoisture absorber 252 has a property of absorbing moisture and releasingthe absorbed moisture when the temperature of the second moistureabsorber 252 reaches a predetermined temperature range by heating.Zeolite is used for the second moisture absorber 252. Zeolite has ahigher moisture absorbing property than mesoporous silica and has aproperty of releasing the absorbed moisture at a temperature (around 100degrees) higher than the temperature at which the regeneratingmesoporous silica is regenerated.

According to the first preferred embodiment of the present invention,the ECU 13 controls the operation of various devices of the airconditioner 20. The ECU 13 controls the operations of the first andsecond blowers 23, 31, the first through fourth valves 26, 27, 35, 36,signals of the first through third temperature sensors 28, 29, 38 andthe humidity sensors 37A, 37B and the rotation of the electric motor223. The ECU 13 includes a memory (not shown) storing a program used formaking various determinations based on signals from the first throughthird temperature sensors 28, 29, 38 and the humidity sensors 37A, 37Bto select at least one of the first and second desiccant devices 22, 25used for dehumidification.

Flowchart of FIG. 3 shows steps of operation for controllingdehumidification in accordance with the condition of dehumidifying loaddetected by the first and third temperature sensors 28, 38 and also thepresence or the magnitude of exhaust heat generated by the system heatsources such as the electric motor 11 and detected by the secondtemperature sensor 29. The dehumidifying load means a load of airconditioner for dehumidification, which is in general, high under a hightemperature and high humidity condition, and low under a low temperatureand low humidity condition. The following will describe the steps ofoperation for controlling with reference to the flowchart shown in FIG.3. At step S1, the humidity in the interior R is measured by thehumidity sensor 37A for determining whether or not dehumidification ofthe air in the interior R is required. If NO at the step S1, on theother hand, the operation of the dehumidification is stopped, and theprocess of the flowchart ends. If YES at the step S1, it is determinedwhich of drawing in of external air and internal air circulation isrequired at step S2. If it is determined at the step S2 that intake ofexternal air should be done, the temperature T1 is measured by the firsttemperature sensor 28 and the temperature T2 of the system heat sourcesis measured by the second temperature sensor 29 at step S3. At step S4,the ECU 13 determines which region of A through C indicated in thetemperature data map shown in FIG. 4 includes the measured temperatureT1 and the temperature T2.

If it is determined at the step S2 that the internal air circulationshould be done, the temperature T3 is measured by the third temperaturesensor 38, and the temperature T2 of the system heat source is measuredby the second temperature sensor 29 at step S5. At step S6, the ECU 13determines which region of A through C includes the temperature T3 andthe temperature T2.

Following the steps S4, S6, it is determined at step S7 whether or notthe temperature T2 is higher than the temperature Tb and temperature T1(or the temperature T3) falls within the region A of the temperaturedata map of FIG. 4 based on the measured temperature T1 (or thetemperature T3) and the temperature T2. When the temperature of exhaustheat is lower than the temperature Tb, the first and second desiccantdevices 22, 25 may not be regenerated by the exhaust heat. According tothe first preferred embodiment of the present invention, the temperatureTb is set at 40 degrees. Depending on the material of the first andsecond moisture absorbers 222, 252, the setting of the exhaust heattemperature Tb is changed. If it is determined at step S7 that thetemperature T1 (or the temperature T3) falls in the region A, the firstvalve 26 is opened and the second valve 27 is closed, the first andsecond blowers 23, 31 are activated, and the electric motor 223 isdriven at step S8. At step S9, therefore, the first desiccant device 22humidifies external air flowing through the air passage 21 while beingregenerated by exhaust heat generated by the system heat sources. Theprocess goes back to the step S1.

If it is determined at the step S7 that the temperature T1 (or thetemperature T3) does not fall within the region A, it is determined atstep S10 whether or not the temperature T1 (or the temperature T3) fallswithin the region B. The region B is a region where the temperature T1(or the temperature T3) is relatively high and the temperature T2 ishigher than the temperature Tb. If it is determined at the step S10 thatthe temperature T1 (or the temperature T3) falls within the B region,the first and second valves 26, 27 are opened, the first and secondblowers 23, 31 are activated, and the electric motor 223 is driven atstep S11. At step 12, external air (or air flowing from the interior Rthrough the internal air passage 34) flows through both of the first andsecond desiccant devices 22, 25, thereby being dehumidified. The processthen goes back to the step S1.

If it is determined at the step S10 that the temperature T1 (or thetemperature T3) does not fall within the region B, it is determined atstep S13 whether or not the temperature T1 (or the temperature T3) fallswithin the region C. The region C is a region where the temperature T2(or the temperature T3) is lower than the temperature Tb. If it isdetermined at the step S13 that the temperature T1 (or the temperatureT3) falls within the region C, the first valve 26 is closed and thesecond valve 27 is opened, and only the first blower 23 is activated atstep S14. Thus, at step 15, external air (or air flowing from theinterior R through the internal air passage 34) flows through the seconddesiccant device 25, thereby being dehumidified. If it is determined atthe step 13 that the temperature T1 (or the temperature T3) falls withinthe region C, it is determined at step S16 that dehumidification may notbe performed, and then the process ends. Thus, according to any one ofthe regions A through C in the temperature data map shown in FIG. 4within which the temperature falls, the desiccant device to be used fordehumidification is selected to dehumidify external air (or air flowingfrom the interior R through the internal air passage 34). If it isdetermined at the step S7 that the humidifying condition falls withinthe region A, the air conditioner 20 is operated in a normal operationmode. If the humidifying condition falls within the region B or region Cin the step S10, or S13, the temperature T1 (or the temperature T3) andthe temperature T2 are measured constantly for determining whether ornot the humidifying condition falls within the region A. By socontrolling the operation of the air conditioner 20, the time ofoperation of the second desiccant device 25 is minimized.

The following will describe in detail the temperature data map shown inFIG. 4. The temperature data map shows the relation between thetemperature T1 (or the temperature T3) and the temperature T2, and thedata of the temperature data map is stored in the memory of the ECU 13.In the region A of the temperature data map, the dehumidification may beperformed by the first desiccant device 22, and the first desiccantdevice 22 may be regenerated. In other words, when the dehumidifyingcondition falls within the region A of the temperature data map, thedehumidifying load is so low that dehumidification may be performed onlyby the first desiccant device 22 and the exhaust heat for regeneratingthe first desiccant device 22 exists. If the dehumidifying conditionfalls within the region A of the temperature data map, no air is allowedto flow through the branched air passage 24. When the border between theregions A and B shown in the temperature data map of FIG. 4 representsthreshold temperature Tc serving as a first threshold value andthreshold temperature Tb serves as a second threshold value, the regionA fulfills following two equations. The first threshold value representsmost amount of a dehumidifying load to dehumidifying the air by thefirst desiccant device 22 and the second threshold value is thelowermost temperature required for regenerating the first moistureabsorber 222.

T2>Tb

T2>A(T 1−Tc),

wherein A is a constant representing the gradient of the border.

In other words, allowing the air to flow through the branched airpassage 24 is determined by a linear function of a differential betweenthe temperature (T1) of the air and the first threshold value (Tc), andthe second threshold value (Tb) is a constant.

When the dehumidifying condition falls within the region B of thetemperature data map, the dehumidification may not be performed only bythe first desiccant device 22, and the first desiccant device 22 may beregenerated. Thus, when the dehumidifying condition falls within theregion B, the dehumidification is required to be performed by the seconddesiccant device 25 in addition to the first desiccant device 22. Inother words, in the region B, the dehumidifying load is so high thatdehumidification can be performed by the first and second desiccantdevices 22, 25, and exhaust heat for regenerating the first desiccantdevice 22 exists.

When the dehumidifying condition falls within the region C of thetemperature data map, the dehumidification may be performed by thesecond desiccant device 25, and the first desiccant device 22 may not beregenerated. In other words, in the region C, the dehumidifying load isof such an extent that the dehumidification is performed by the seconddesiccant device 25, and no exhaust heat for regenerating the firstdesiccant device 22 exists. The dehumidification may not be performed bythe first desiccant device 22 and, therefore, the dehumidification ofexternal air is required to be performed only by the second desiccantdevice 25. When the dehumidifying condition falls within the region B orC, air is allowed to flow through the branched air passage 24, and theregions B and C fulfill following three equations.

T1<Ta

T2<Tb

T2<A(T1−Tc)

If the temperature T1 (or the temperature T3) is higher than thetemperature Ta in the temperature data map, the dehumidification may notbe performed regardless of the existence of the exhaust heat. Thetemperature Ta serves as a third threshold value. For example, thetemperature Ta in the temperature data map is the temperature forregeneration of the second moisture absorber 252 of the second desiccantdevice 25. The temperature Ta shown in FIG. 4 is the upper limit oftemperature of the air to be dehumidified by the second desiccant device25. If the temperature T1 of the air is higher than the temperature Tawhich is higher than the first threshold value Tc and is a lowermosttemperature required for regenerating the second moisture absorber 252,no air is allowed to flow through the air passage 21 and the thebranched air passage 24. The temperature for regenerating the secondmoisture absorber 252 is increased with an increase of the temperatureof air to be dehumidified by the second moisture absorber 252. Using thesecond moisture absorber 252 having a moisture absorbing capacity thatis too high for the environment in which the vehicle is used isdisadvantageous in supplying of heat. Thus, in selecting the secondmoisture absorber 252, the upper limit temperature of air to bedehumidified by the moisture absorbing of the second moisture absorber252 may be determined with the vehicle usage environment taken intoconsideration so that the dehumidification may not be performed. In thiscase, it is determined that dehumidifying condition falls within theregion C at the step S13, so that the process may skip the step S16where it is determined that the dehumidification may not be performed.Region A where the temperature T2 is lower than the temperature Tb isthe region where exhaust heat generated by the system heat sources forregenerating the first moisture absorber 222 of the first desiccantdevice 22 does not exist regardless of the temperature T1 (or thetemperature T3), and the first desiccant device 22 may not be used. Inthe first preferred embodiment of the present invention, the temperaturedata map shown in FIG. 4 is used for explaining two relations betweenthe temperature T1 and the temperature T2 and between the temperature T3and the temperature T2, but two different temperature data maps may bemade for the two relations. In addition, the border between the regionsA and B has the gradient angle A. Alternatively, it may be determinedthat dehumidifying condition falls within the region A or B bydetermining whether or not the temperature T1 is higher than the firstthreshold value.

The following will describe in detail the regeneration of the seconddesiccant device 25. The regeneration of the second desiccant device 25should preferably be performed during a stop state of the vehicle 10,such as during charging the battery 14 by the external power source 18.When regenerating the second desiccant device 25, the first valve 26 isclosed, the second valve 27 is opened, and the first blower 23 isactivated to rotate in reverse direction. The heater 33 is operated toheat the air introduced into the air passage 21 from the interior R andthe heated air is flowed through the second desiccant device 25 forregenerating the second moisture absorber 252. Moisture released fromthe second moisture absorber 252 by regenerating the second moistureabsorber 252 is discharged out into the exterior S through the firstblower 23. Thus, the second moisture absorber 252 is regenerated duringa time other than the time of the dehumidification of air.

The following will describe in detail the operation of the airconditioner 20. The air conditioner 20 according to the first preferredembodiment of the present invention is activated by button operation byan operator or by controlling of the ECU 13 based on predeterminedprogram. Firstly, the humidity of the interior R is measured by thehumidity sensor 37A to determine whether or not dehumidification isrequired. Then, if it is determined that the dehumidification isrequired, it is then determined which of drawing in of external air andinternal air circulation is required.

The following will describe the steps to take when the external airneeds to be drawn in. If the ECU 13 determines based on the temperatureT1 and the temperature T2 measured during driving operation of thevehicle 10 that the dehumidifying condition falls within the region Abecause of a condition of dehumidifying load and existence of theexhaust heat of the system heat sources, the first valve 26 is openedand the second valve 27 is closed. Then, the first and second blowers23, 31 are activated, and the electric motor 223 is driven to rotate thefirst moisture absorber 222 of the first desiccant device 22. Externalair to be dehumidified is introduced into the air passage 21 and flowedthrough the first moisture absorber 222, as shown in FIG. 5A. Theexternal air is dehumidified while being passed through the firstmoisture absorber 222. The dehumidified air is further passed throughthe air passage 21 and introduced into the interior R. Meanwhile, air inthe interior R is introduced into the regeneration air passage 30, andheated by exhaust heat generated in the electric power device 19, suchas the electric motor 11 and the inverter 12. The heated air is flowedthrough the first desiccant device 22 at the position opposite to theposition connected to the air passage 21 of the rotary shaft 224, andmoisture is removed from the first moisture absorber 222 and the firstmoisture absorber 222 is regenerated. Air containing removed moisture isdischarged out to the exterior S. The part of the first moistureabsorber 222 which has been regenerated is rotated to be used fordehumidification. Thus, dehumidification and regeneration of the firstmoisture absorber 222 are performed continuously.

If the ECU 13 determines that the dehumidifying condition falls withinthe region B from a condition of dehumidifying load and existence of theexhaust heat of the system heat sources, the first and second valves 26,27 are both opened. The first and second blowers 23, 31 are activatedand the electric motor 223 is driven to rotate the first moistureabsorber 222. External air is introduced into and flowed through the airpassage 21 by the rotation of the first moisture absorber 222, as shownin FIG. 5B. The external air introduced into the air passage 21 isdivided at the branch point P into two flows, one flowing through thefirst desiccant device 22 and the other flowing through the branched airpassage 24 and the second desiccant device 25. The external air flowingthrough the rotating first moisture absorber 222 and the second moistureabsorber 252 is dehumidified by the first and second moisture absorbers222, 252, respectively.

The air dehumidified by the first and second desiccant devices 22, 25 ismerged together at the point Q and flowed through the air passage 21 andintroduced into the interior R. Meanwhile, the air having a hightemperature is flowed through the regeneration air passage 30 forheating the first moisture absorber 222. Thus, moisture is removed fromthe first moisture absorber 222 and the first moisture absorber 222 isregenerated. Since the moisture absorbing capacity of the secondmoisture absorber 252 is higher than that of the first moisture absorber222, dehumidification under a high load can be accomplished moreeffectively by the first and second desiccant devices 22, 25 than by thefirst desiccant device 22 alone.

If the ECU 13 determines that the dehumidifying condition falls withinthe region C because of a condition of dehumidifying load and existenceof the exhaust heat of the system heat sources, the first valve 26 isclosed, and the second valve 27 is opened. The second blower 31 is at astop, and the first blower 23 is activated. Thus, external air fordehumidification is introduced through the air passage 21 into thebranched air passage 24 and then flowed through the second desiccantdevice 25, as shown in FIG. 5C. The air is passing through anddehumidified by the second moisture absorber 252 of the second desiccantdevice 25. Then, the dehumidified air is introduced through the point Qand the air passage 21 into the interior R. During this operation, thefirst desiccant device 22 is not operated.

The following will describe the regeneration of the second desiccantdevice 25 during a stop state of a vehicle. The second moisture absorber252 of the second desiccant device 25 is regenerated during charging thebattery of the vehicle, as shown in FIG. 5D. That is, regeneration ofthe second moisture absorber 252 is performed during the time other thanwhen dehumidification is performed by the first and second desiccantdevices 22, 25. While the second moisture absorber 252 is beingregenerated, the first valve 26 is closed, the first blower 23 isoperated to rotate in reverse direction, and the heater 33 is activated.Air in the interior R is introduced from the air passage 21 into thebranched air passage 24 due to the reverse rotation of the first blower23. The air introduced into the branched air passage 24 is heated by theheater 33 which is then in an energizing state. The heated air is flowedthrough the second desiccant device 25, so that the second moistureabsorber 252 is heated and moisture is removed therefrom. The aircontaining the removed moisture is discharged out from the branched airpassage 24 into the exterior S through the branch point P and the airpassage 21.

The following will describe the case when regeneration of the firstmoisture absorber 222 by the exhaust heat generated by the system heatsources is not enough to fulfill the demand of dehumidifying theexternal air by the first desiccant device 22. When the humiditymeasured by the humidity sensor 37B excesses a predetermined valueduring dehumidifying air by the first desiccant device 22, the ECU 13determines that the first moisture absorber 222 has very little moistureabsorbing capacity. Then, the ECU causes the first valve 26 to be closedand the second valve 27 to be opened. Therefore, the regeneration of thefirst moisture absorber 222 by exhaust heat generated by the system heatsources is continued with the flow of the air to the first desiccantdevice 22 shut off, as shown in FIG. 6A. Then, the air fordehumidification is introduced into and flowed through the branched airpassage 24 and dehumidified by the second desiccant device 25. Thedehumidified air is introduced into the interior R through the point Q.In this case, no air is dehumidified by the first moisture absorber 222,and only the regeneration is performed by exhaust heat of the systemheat sources. Therefore, the moisture absorbing capacity of the firstmoisture absorber 222 is restored by the regeneration of the firstmoisture absorber 222. In a case no air is dehumidified by the first andsecond desiccant devices 22, 25 as shown in FIG. 6B, the regeneration ofthe first moisture absorber 222 may be performed by exhaust heat of thesystem heat sources.

The first preferred embodiment offers the following advantageouseffects.

-   (1) Based on the temperature of air to be dehumidified and the    system heat sources, air is dehumidified by at least one of the    first and second desiccant devices 22, 25. Then, the dehumidified    air is supplied to the interior R. During the dehumidification of    air by the first desiccant device 22, the regeneration of the first    moisture absorber 222 is performed simultaneously by the exhaust    heat of the system heat sources. During the dehumidification of air    by the second desiccant device 25, regeneration of the second    moisture absorber 252 is not performed. When the dehumidifying load    is low due to the temperature of air to be dehumidified and the    exhaust heat of the system heat sources for regenerating the first    desiccant device 22 exists, air conditioning may be performed while    dehumidifying air only by the first desiccant device 22. Thus, the    regeneration of the first desiccant device 22 is performed by    effectively utilizing low-temperature exhaust heat generated by the    electric motor 11 and the inverter 12. That is, dehumidification may    be performed continuously even if the temperature of the exhaust    heat of the system heat sources is low. If it is determined that the    dehumidifying load is relatively high, but heat for regenerating the    first desiccant device 22 exists, dehumidification may be performed    by the first desiccant device 22 and the second desiccant device 25    which has higher dehumidifying capacity than the first desiccant    device 22. If it is determined that the dehumidifying load is in the    range in which dehumidification may be performed by the first    desiccant device 22, but heat for regeneration of the first    desiccant device 22 does not exits, air conditioning may be    performed while dehumidifying air only by the second desiccant    device 25. Thus, the air conditioner of the first preferred    embodiment offers stable dehumidifying operation in a wide range of    temperatures regardless of the environment surrounding the vehicle.-   (2) The ECU 13 is informed of a condition of the dehumidifying load    and existence of heat for regenerating the first desiccant device 22    from the temperature of air detected by the first temperature sensor    28 and the temperature of exhaust heat of the electric power device    19 detected by the second temperature sensor 29. Thus, the ECU 13    can control airflow in the air passages 21, 24 in accordance with a    condition of the dehumidifying load and existence of heat for    regeneration.-   (3) The ECU 13 can control the airflow through the air passage 21 by    controlling the operation of the first valve 26 and also the airflow    through the branched air passage 24 by controlling the operation of    the second valve 27.-   (4) Since the vehicle 10 having the air conditioner 20 uses external    electrical power for charging battery supplied from the external    electrical power source, regeneration of the second moisture    absorber 252 may be performed while the air conditioner 20 is at a    stop and, therefore, no dehumidification is done for the first and    second desiccant devices 22, 25. The battery 14 on the vehicle    connected to the external power source 18 through the battery    charger 17 may be used for supplying power to the heater 33 during a    stop state of the vehicle without affecting the battery charging    operation. Through the heater 33 is operated by and consumes    electric power, the electric power in the battery 14 is not consumed    since the electric power for the heater 33 may be supplied from the    external power source 18.-   (5) The first moisture absorber 222 containing at least one of    mesoporous silica and silica gel may be regenerated at a lower    temperature than the second moisture absorber 252 containing    zeolite. The second moisture absorber 252 which has higher moisture    absorbing capacity than the first moisture absorber 222 offers    higher dehumidifying property.

The following will describe an air conditioner 40 according to a secondpreferred embodiment of the present invention with reference to FIGS.7A, 7B, 8A and 8B. In the air conditioner 40 according to the secondpreferred embodiment of the present invention shown in FIG. 7A, commonor similar elements or parts are designated by the same referencenumerals as those of the first preferred embodiment and, therefore, thedescription thereof will be omitted. According to the first preferredembodiment of the present invention, the first desiccant device 22 isregenerated by exhaust heat generated by the system heat sources.According to the second preferred embodiment of the present invention,reaction heat generated in dehumidification of the second desiccantdevice 25 is used for regeneration of the first desiccant device 22.Thus, the system heat source according to the second preferredembodiment of the present invention includes the second desiccant device25.

Referring to FIG. 7A, a regeneration air passage 41 is provided betweenthe electric power device 19 and the first desiccant device 22. Athree-way valve 42 is disposed at a junction between the regenerationair passage 30 and the regeneration air passage 41. The ECU 13 controlsthe operation of the three-way valve 42 to change the air passage, sothat air from the electric power device 19 is flowed toward theregeneration air passage 30 or the regeneration air passage 41. A heatexchanger 43 is disposed in the regeneration air passage 41.

Another heat exchanger 44 is disposed between the second desiccantdevice 25 and the point Q in the branched air passage 24. A heat pipe 45is provided for connection between the heat exchangers 43, 44. The heatexchangers 43, 44 and the heat pipe 45 form the reaction heat supplierof the present invention. The heat pipe 45 is thermally connected to thebranched air passage 24 where the dehumidified air by the seconddesiccant device 25 flows. The heat pipe 45 includes a pipe body made ofmetal such as aluminum or copper having a high thermal conductivity andhas a closed space (not shown) formed therein. The pipe body of the heatpipe 45 has in the space thereof wick (not shown) having capillaryaction and refrigerant gas (not shown) having characteristics of beingevaporated and condensed in a narrow range of temperature.

According to the air conditioner 40 of the second preferred embodimentof the present invention, if the ECU 13 determines that thedehumidification condition falls within the region A because of acondition of dehumidifying load and existence of the exhaust heatgenerated by the system heat sources, dehumidification is performed onlyby the first desiccant device 22, as in the case of the first preferredembodiment. In this case, since the first moisture absorber 222 may beregenerated by exhaust heat of the system heat sources, the three-wayvalve 42 is operated so as to prevent air from the electric power device19 from flowing into the regeneration air passage 41, but to allow airfrom the electric power device 19 to flow through the regeneration airpassage 30 toward the first desiccant device 22. Thus, the firstmoisture absorber 222 is regenerated by the exhaust heat of the systemheat sources.

If the ECU 13 determines that the dehumidifying condition falls withinthe region B because of a condition of the dehumidifying load andexistence of the exhaust heat of the system heat sources, air isdehumidified by the combination of the first and second desiccantdevices 22, 25. In this case, since the first moisture absorber 222 maybe regenerated by the exhaust heat of the system heat sources, thethree-way valve 42 is positioned such that air from the electric powerdevice 19 is introduced into the regeneration air passage 41. Thus, theair from the electric power device 19 is flowed to the first desiccantdevice 22 through the regeneration air passage 30. Therefore, the firstmoisture absorber 222 is regenerated by the exhaust heat of the systemheat sources.

If the ECU 13 determines that the dehumidifying condition falls withinthe region C because of a condition of the dehumidifying load andexistence of the exhaust heat of the system heat sources, the three-wayvalve 42 is positioned so as to allow air to be introduced from theelectric power device 19 into the regeneration air passage 41. Duringdehumidification of air by the second desiccant device 25, reaction heatis generated due to the moisture absorbing by the second moistureabsorber 252, so that the dehumidified air in the branched air passage24 is heated by the reaction heat. The heat of the dehumidified air isexchanged by the heat exchanger 44 to be transmitted to the heat pipe45. The heat transmitted to heat pipe 45 is further transmitted rapidlyto the heat exchanger 43, where air flowing through the regeneration airpassage 41 is heated by the heat of the heat pipe 45 through heatexchanging. The air heated by the heat exchanging is flowed through thefirst desiccant device 22 and used for regenerating the first moistureabsorber 222.

According to the air conditioner 40 of the second preferred embodimentof the present invention, the reaction heat generated during thedehumidification of the second desiccant device 25 may be utilized as aheat source for regeneration of the first moisture absorber 222.According to the first preferred embodiment of the present invention,the temperature of the exhaust heat of the system heat sources is low inthe region C of the temperature data map of FIG. 4 and, therefore, airdehumidification by the first desiccant device 22 cannot be performed.According to the second preferred embodiment of the present invention,however, air dehumidification by the first desiccant device 22 and theregeneration of the first moisture absorber 222, as well as the airdehumidification by the second desiccant device 25, may be performed. Inother words, according to the second preferred embodiment of the presentinvention, controlling for air dehumidification used for the region Bmay be used also in the region C where the temperature of the exhaustheat of the system heat sources is relatively low, with the result thatthe range of the region B is expanded. As shown in FIG. 7B, thethree-way valve 42 may be substituted with a valve 42A disposed in theregeneration air passage 30 and a valve 42B disposed in the regenerationair passage 41.

According to the second preferred embodiment of the present invention,the regeneration of the first desiccant device 22 is regenerated by thereaction heat generated in the dehumidification of the second desiccantdevice 25 by using the heat pipe 45. Alternatively, as shown in FIG. 8A,heat exchanging is performed between the regeneration air passage 46 andthe branched air passage 24 to transfer the reaction heat generated inthe second desiccant device 25. The air conditioner 40 shown in FIG. 8Ahas a heat exchanger 47 for heat exchanging between the branched airpassage 24 and the regeneration air passage 46. In this structure, theregeneration air passage 46 and the heat exchanger 47 form the reactionheat supplier of the present invention. The reaction heat generated inthe dehumidification of the second desiccant device 25 is transferred bythe dehumidified air flowing through the branched air passage 24. Whenthe three-way valve 42 is positioned such that air is flowed through theregeneration air passage 46, heat exchanging is performed in the heatexchanger 47 between the dehumidified air flowing through the branchedair passage 24 and the air flowing through the regeneration air passage46. Thus, heat is transferred from the dehumidified air to the air inthe regeneration air passage 46 by the heat exchanging and the heat iscarried by the air in the regeneration air passage 46 and transferred tothe first desiccant device 22. In this case, in the region C of thetemperature data map, the dehumidification by the first desiccant device22 and the regeneration of the first moisture absorber 222 may beperformed in addition to the dehumidification by the second desiccantdevice 25, without using the heat pipe 45. As shown in FIG. 8B, thethree-way valve 42 may be substituted with a valve 42A disposed in theregeneration air passage 30 and a valve 42B disposed in the regenerationair passage 41.

The following will describe an air conditioner 50 according to a thirdpreferred embodiment of the present invention with reference to FIG. 9.In the air conditioner 50 according to the third preferred embodiment ofthe present invention shown in FIG. 9, common or similar elements orparts are designated by the same reference numerals as those which areused for the air conditioner 20 of the first preferred embodiment and,therefore, the description thereof will be omitted. According to thefirst and second preferred embodiments, the first desiccant device 22 isdisposed in the air passage 21, the second desiccant device 25 isdisposed in the branched air passage 24 branched from the air passage21, the dehumidified air flowing in the branched air passage 24 ismerged with the dehumidified air in the air passage 21 and supplied tothe interior R. The air conditioner 50 according to the third preferredembodiment has two air passages 51, 54 provided separately withoutmerging with each other, and the first and second desiccant devices 22,25 are disposed in the air passages 51, 54, respectively.

As shown in FIG. 9, the first air passage 51 and the second air passage54 connect the exterior S to the interior R, respectively. The first airpassage 51 has an inlet 51A serving as the first inlet and an outlet 51Bserving as the first outlet. The inlet 51A is communicable with theexterior S, and the outlet 51B is communicable with the interior R as aspace for air conditioning. Similarly, the second air passage 54 has aninlet 54A serving as the second inlet and an outlet 54B serving as thesecond outlet. The inlet 54A is communicable with the exterior S of thevehicle, and the outlet 51B is communicable with the interior R. Thefirst temperature sensor 58, the first blower 53, the first valve 56 andthe first desiccant device 22 are disposed in the first air passage 51in this order from the exterior S toward the interior R. The thirdblower 55, the second valve 57, the second desiccant device 25 and theheater 33 are disposed in the second air passage 54 in this order fromthe exterior S toward the interior R. In the third preferred embodiment,a second blower 59 is disposed between the interior R and the electricpower device 19 in the regeneration air passage 30. The firsttemperature sensor 58, the first blower 53, the first valve 56, thethird blower 55, the second valve 57, the second blower 59 and theelectric motor 223 are electrically connected to the ECU 13. In thethird preferred embodiment, the first blower 53, the second blower 59,the second valve 57 and the third blower 55 form the airflow controllerof the present invention. The first temperature sensor 58 serves as theair temperature sensor of the present invention.

In the third preferred embodiment, the first air passage 51 and thesecond air passage 54 are disposed separately. As in the case of thefirst embodiment, however, the dehumidification is performed by thefirst desiccant device 22 and the second desiccant device 25 based onthe temperature data map shown in FIG. 4 and using the steps of theflowchart shown in FIG. 3.

As compared to the first preferred embodiment of the present invention,the number of the blowers used in the third preferred embodiment isincreased by one, but the arrangement of the air passage may besimplified without having a branched point or a merging point.

In the third preferred embodiment, switching of air to be supplied tothe first or second desiccant device 22, 25 is controlled independentlyby the first blower 53 or the third blower 55 and, therefore, the firstand second valves 56, 57 may be omitted.

The present invention is not limited to the above-described firstthrough third embodiments but may be variously modified within the scopeof the invention. The first though third embodiments may be modified asexemplified below.

In the first through third preferred embodiments of the invention, theair conditioner is applied to an electric vehicle. However, the airconditioner is also applicable to a PHEV. Furthermore, the airconditioner is applicable to a hybrid electric vehicle (HEV) exceptingthe PHEV. If the air conditioner is applied to PHEV or HEV, exhaust heatgenerated by an engine may be used as the heat for regenerating thesecond desiccant device during driving of the vehicle when the seconddesiccant device is not being dehumidified.

The present invention is advantageous particularly in an electricvehicle having no internal combustion engine and, therefore, having noexhaust heat available for regeneration of the moisture absorber.

In the first through third preferred embodiments of the presentinvention, the first desiccant device is of a rotor type in whichdehumidification and regeneration may be simultaneously performed. Thefirst desiccant device is not limited to the rotor type, but it may ofany type as long as the dehumidification and regeneration may besimultaneously performed. For example, the first desiccant device mayhave in the case thereof a plurality of moisture absorbers, an airpassage operable to switch the introduction of air to be dehumidifiedand a regeneration air passage operable to switch the introduction ofregenerating air. In the first desiccant device having this structure,dehumidification and regeneration carried out simultaneously byperforming air dehumidification at any moisture absorber in thedesiccant device, and simultaneously performing regeneration of anothermoisture absorber which is not used for the air dehumidification.

In the first through third preferred embodiments of the presentinvention, air for regeneration of the second desiccant device 25 isdischarged to the vehicle exterior. Alternatively, heat of the air forregeneration of the second desiccant device 25 may be used for heatingof the vehicle interior. In such a case, an additional air passage 61 isprovided for connection between the exterior S to the interior R, and aheat exchanger 62 is disposed between the second desiccant device 25 inthe branched air passage 24 and the exterior S for exchanging heat withthe air in the air passage 61. In this structure, external airintroduced into the air passage 61 is heated in the heat exchanger 62 byexchanging heat with the air flowing through the branched air passage 24and then the heated air is introduced into the interior R. According tothe air conditioner of this structure, heating of the interior R may beperformed preciously before driving. FIG. 10 shows an example of thestructure which is applied to the first preferred embodiment of thepresent invention, and it is also applicable to the second and thirdpreferred embodiments of the present invention. Heat exchangers may beadditionally provided in the structure shown in FIG. 10. Specifically,as shown in FIG. 11, a heat exchanger 63 is disposed between the firstdesiccant device 22 in the regeneration air passage 30 and the exteriorS, and another heat exchanger 64 is disposed between the point Q in theair passage 21 and the interior R, an air circulation path 65 is formedfor circulating air between the heat exchangers 63, 64. In the airconditioner of FIG. 10, air dehumidified by the first desiccant device22 may be heated by exhaust heat generated during regeneration of thefirst desiccant device 22, and such heated dehumidified air may be usedfor heating of the interior R.

In the first through third preferred embodiments of the presentinvention, mesoporous silica is used for the first moisture absorber,and zeolite is used for the second moisture absorber. However,mesoporous silica and zeolite need not necessarily be used for the firstmoisture absorber and the second moisture absorber, respectively. Forexample, a moisture absorbing material made by adjusting the propertiesof mesoporous silica, zeolite or silica gel may be used for the firstand second moisture absorbers. Thus, the moisture absorbing material maybe formed such that the moisture absorbing property of the firstmoisture absorber is less than that of the second moisture absorber, butoperable to switch the introduction of air to be dehumidified.

In the first through third preferred embodiments, the temperature datamap shown in FIG. 4 includes the region C where the dehumidificationcannot be performed. If the second desiccant device is made of amoisture absorbing material having sufficient dehumidifying capacitywithin the range of assumed temperatures under which vehicle is used,the region C may be omitted. In this case, the step S13 is no morenecessary, so that determination at the step S10 may be omitted.

In the first through third preferred embodiments of the presentinvention, the temperatures of the system heat sources are determined bydirect measurement, but the temperature determination is not limiteddirect measurement. If the system heat source is an electrical device,electric current that flows through the electrical device may bemeasured, so that the temperatures of the system heat sources may beestimated from the measured electrical current.

In the first preferred embodiment of the present invention, it isdetermined whether or not the dehumidification of air in the vehicleinterior is required based on the humidity measurements provided by thehumidity sensor. Alternatively, a switch for starting dehumidificationmay be provided in the air conditioner, so that the air conditioner isactivated by operating the switch. In this case, the requirement fordehumidification of air in the vehicle interior is determined by avehicle occupant. If the vehicle occupant determines that thedehumidification is required, the switch is turned on and thedehumidification of air in the vehicle is performed by the airconditioner.

In the first preferred embodiment of the present invention, the humiditysensor 37B is disposed between the first desiccant device 22 and thepoint Q in the air passage 21. Alternatively, a temperature sensorconnected to the ECU may be disposed upstream of or downstream of thefirst desiccant device 22 in the air passage 21 as viewed in the airflowing direction in the air passage 21. Reaction heat is generated inthe humidification. If the first desiccant device 22 has a sufficienthumidifying capacity, temperature difference occurs in the air betweenbefore and after the dehumidifying. If the temperature differenceexceeds a predetermined value, it may be determined that theregeneration of the first moisture absorber 222 is not sufficientlyperformed by exhaust heat of the system heat sources, and, in such acase, the second desiccant device 25 may be operated. The firsttemperature sensor may be used as a temperature sensor for measuring thetemperature of air before being dehumidified by the first desiccantdevice 22. The temperature sensor may be disposed upstream or downstreamof the first desiccant device 22 with respect to the air flowingdirection in the air passage 21 in the second and third preferredembodiments of the present invention.

1. An air conditioner comprising: a first air passage having a firstinlet and a first outlet communicable with a space to be airconditioned; a first desiccant device having a first desiccant material,the first desiccant device disposed in the first air passage; a secondair passage having a second inlet and a second outlet communicable withthe space; a second desiccant device having a second desiccant materialwhose temperature for regeneration is higher than the temperature forregeneration of the first desiccant material, the second desiccantdevice disposed in the second air passage; a system heat source; a heatsupplier supplying heat generated by the system heat source to the firstdesiccant device for regenerating the first desiccant material; a systemheat source temperature sensor for detecting the temperature of thesystem heat source; an airflow controller regulating airflow in thefirst air passage and the second air passage; and a controllercontrolling the airflow controller based on the temperature of thesystem heat source detected by the system heat source temperaturesensor.
 2. The air conditioner according to claim 1, further comprisingan air temperature sensor measuring the temperature of the air flowingto the first desiccant device in the first air passage or thetemperature of the air flowing to the second desiccant device in thesecond air passage, wherein the controller controls the airflowcontroller based on the signals from the system heat source temperaturesensor and the air temperature sensor.
 3. The air conditioner accordingto claim 2, wherein the controller controls the airflow controller suchthat air is allowed to flow through the second air passage if thetemperature of the air is higher than a first threshold value whichrepresents most amount of a dehumidifying load to dehumidify the air bythe first desiccant device or the temperature of the system heat sourceis lower than a second threshold value which is the lowermosttemperature required for regenerating the first desiccant material, andno air is allowed to flow through the second air passage if thetemperature of the air is lower than the first threshold value and thetemperature of the system heat source is higher than the secondthreshold value.
 4. The air conditioner according to claim 3, whereinallowing the air to flow through the second air passage is determined bya linear function of a differential between the temperature of the airand the first threshold value, and the second threshold value which is aconstant.
 5. The air conditioner according to claim 3, wherein thecontroller controls the airflow controller such that no air is allowedto flow through the first air passage and the second air passage if thetemperature of the air is higher than a third threshold value which ishigher than the first threshold value and is the lowermost temperaturerequired for regenerating the second desiccant material.
 6. The airconditioner according to claim 1, further comprising a space airtemperature sensor measuring the temperature of the air in the space,wherein the space air temperature sensor is used in determining which ofthe first desiccant device and the second desiccant device is operated.7. The air conditioner according to claim 1, further comprising ahumidity sensor measuring the humidity of the air in the space, whereinthe humidity sensor is used in determining whether or notdehumidification of air in the space is needed.
 8. The air conditioneraccording to claim 1, wherein the second air passage is branched fromthe first air passage, the first inlet and second inlet or the firstoutlet and the second outlet is common to each other, and the first airpassage and the second air passage including the first desiccant deviceand the second desiccant device are arranged parallel to each other,wherein the airflow controller includes a first valve disposed in thefirst air passage and a second valve disposed in the second air passage,wherein the controller controls airflow in the first air passage and thesecond air passage by controlling the operation of the first valve andthe second valve.
 9. The air conditioner according to claim 1, thesystem heat source includes a second desiccant device which generatesreaction heat during dehumidification, and the heat supplier includes areaction heat supplier supplying the reaction heat to the firstdesiccant device.
 10. The air conditioner according to claim 9, whereinthe reaction heat supplier includes a heat pipe which is thermallyconnected to the second air passage where the dehumidified air by thesecond desiccant device flows.
 11. The air conditioner according toclaim 1, wherein the space is an interior of a vehicle, and the systemheat source is a device radiating waste heat during the device operationon the vehicle except for an internal combustion engine.
 12. The airconditioner according to claim 11, wherein the air conditioner is usedfor the vehicle having a battery charged by external power during a stopstate of the vehicle and the air conditioner further includes a heateroperated to generate heat by the external power for regenerating thesecond desiccant material.
 13. The air conditioner according to claim 1,wherein the first desiccant material contains at least one of mesoporoussilica and silica gel, and the second desiccant material containszeolite.
 14. The air conditioner according to claim 1, wherein the firstdesiccant material is simultaneously regeneratable during thedehumidification of air, and the second desiccant material isregenerated during a time other than the time of the dehumidification ofair.
 15. A method of controlling an air conditioner, the air conditionerincluding: a first desiccant device having a first desiccant material; asecond desiccant device having a second desiccant material whosetemperature for regeneration is higher than the temperature forregeneration of the first desiccant material; and a system heat source,the method comprising the steps of: performing dehumidification of airby at least one of the first desiccant device and the second desiccantdevice based on temperature of the air to be dehumidified andtemperature of the system heat source, regenerating of the firstdesiccant material simultaneously during the dehumidification of the airby the first desiccant device, regenerating the second desiccantmaterial during a time other than when the dehumidification of the airis performed by the second desiccant device; and supplying thedehumidified air to a space to be air conditioned.